Electricity production by metal-air batteries is based on the oxidation of metals, usually aluminum, in the presence of air (O2) and water. Aluminum reacts with oxygen and water to produce aluminum-hydroxide according to the following reaction:4Al+6H2O+3O2→4Al(OH)3+2.71v  (1)However, most of the aluminum-air cells work in a lower voltage than 2.71 volts, typically 0.7 to 1.5 volts, while the rest of the energy is released/dissipated as heat.
Apart of the electricity production chemical reaction, an additional corrosion reaction may take place in the metal-air battery/cell. Some of the aluminum may react with the water to produce aluminum-hydroxide and hydrogen according to the following reaction:2Al+6H2O→2Al(OH)3+3H2  (2)
Both the above reactions take place on the surface of the anode, thus may coat the anode with undesired Al(OH)3 that does not dissolve in water. The building of an Al(OH)3 coating may result in a decrease in the reaction rate and electricity production rate. In order to overcome this deficiency, aluminum-air cells contain alkaline electrolyte in an aqueous solution, such as KOH or NaOH, and an additional reaction that takes place as follows:Al(OH)3+KOH→K++Al(OH)−4  (3)
The salt K++Al(OH)−4 dissolves in water. This reaction allows removal of the Al(OH)3 from the surface of the anode and continuous operation of the cell.
For reaction (3) to effectively remove the Al(OH)3 from the surface of the anode(s) a constant flow of aqueous alkaline solution must reach the anode(s) surfaces. When a plurality of anodes is used and/or the anode has large surface, the constant flow of aqueous alkaline solution may affect the rate of reaction (1) and the rate and efficiency of the electricity production.
The specific energy of an aluminum-air battery is defined as the amount of energy that can be extracted from the cells, divided by the total amount of energy that exists in the aluminum included in the cell. For a given aluminum-air battery/cell, its specific energy may be improved by improving the utilization of the aluminum fuel, for example, by forming substantially constant, and preferably equal flow of the aqueous solution near the anode(s).